The foldable lambdoidal ladder of the prior art comprises front struts, back struts, treads, a folding device and a platform. The platform is a plastic parts directly and pivotally connected to tops of the front struts and back struts, which make the structure between the front strut and the back strut be a rotatable connection. The platform of the lambdoidal is functioned as: 1, connecting the front struts with the bake struts, 2, be a platform in working. Because the plastic parts directly and pivotally connected to the front struts and the back struts, thus it has the following drawbacks: firstly, the connection strength is not strong enough to be a working platform; secondly, the plastic parts pivotally connected both to the front struts and the back struts, which is not convenient in assembly.
And the connection structure between the struts and the treads of the lambdoidal ladder generally have the following two forms: the first one is to lock the strut and the tread by a locking element directly; the second one is to set through holes in the strut, then the ends of the treads inserted into the holes to be locked. The first connection structure has the following drawbacks: firstly, the cut force generated between the tread and the strut is forced entirely on the locking element, therefore the locking member is easy to be broken, and has short use time and lower use safety; secondly, the tread of the prior art generally is hollow structure, therefore, the locking member must locked inside the hollow tread, this is not convenient in locking or assembly; thirdly, the tread may be rotated in use thus the use safety is not enough. The second connecting structure has the following drawbacks: firstly, through holes are set in the struts, thus lower the strength of the struts, if the strength is to be enhanced, it must add the sectional area of the struts or use solid structure, which will add the amount of the material and add the cost of production; secondly, the structure of the treads of the prior art are mostly hollow, the locking member is locked inside the hollow tread, thus both the locking and the assembly are not convenient.